Using RgPublish /target makes no sense in dynamic environment (where folder name is being generated and created dynamically, say by TeamCity). There is no way to pre-create such folder so it must create it by itself.

At the moment, the target folder is taken exactly as specified, and that's where the resulting .nupkg ends up.
Could you clarify a little more your use-case regarding integration with Team City?
I assume that if team city has created an output folder, this may be accessible through some sort of variable you could pass through to RGPublish?

TeamCity creates %system.teamcity.build.workingDir% that I can use. But this is a root of the whole checkout and build process.
If I want use more specific subfolder that doesn't exist in source, I can't, because DM won't create it.